Practicing Success
If $g(x)=\left(x^2+2 x+3\right) f(x), f(0)=5$ and $\lim\limits_{x \rightarrow 0} \frac{f(x)-5}{x}=4$, then g'(0) is equal to |
22 20 18 none of these |
22 |
We have, $f(0)=5$ and $\lim\limits_{x \rightarrow 0} \frac{f(x)-5}{x}=4$ ∴ $\lim\limits_{x \rightarrow 0} \frac{f(x)-5}{x}=4$ $\Rightarrow \lim\limits_{x \rightarrow 0} \frac{f(x)-f(0)}{x}=4 \Rightarrow f'(0)=4$ Now, $g(x)=\left(x^2+2 x+3\right) f(x)$ $\Rightarrow g'(x)=(2 x+2) f(x)+\left(x^2+2 x+3\right) f'(x)$ $\Rightarrow g'(0)=2 f(0)+3 f'(0)=2 \times 5+3 \times 4=22$ |